The process, from Rice University, uses a catalytic reactor and carbon dioxide is used as the feedstock. By using carbon dioxide these types of reactors will help to facilitate ‘green’ chemical synthesis. The prototype reactor and associated process can produce highly purified and high concentrations of formic acid.This means a scaled-up reactor could provide the basis for commercial carbon dioxide conversion technologies.
In tests the new electrocatalyst has demonstrated an energy conversion efficiency of around 42 percent, where close to half of the electrical energy can be stored in formic acid as liquid fuel. The formic acid was generated over a period of 100 hours. To advance the process, the researchers needed to develop a two-dimensional bismuth catalyst and the second a solid-state electrolyte capable of eliminating the need for salt as part of the reaction.
A key advance with the reactor is that while it is possible to create catalysts on the milligram or gram scales, the scientists managed to produce such catalysts at the kilogram scale, allowing for scale-up. The use of X-ray absorption spectroscopy allowed the researchers to assess the reaction in real-time and then to use the data to assess where improvements could be made.
A second aspect was the design of is polymer-based solid electrolyte. These are conventionally coated with sulfonic acid ligands so that the electrode conducts a positive charge as well as having amino functional groups to conduct negative ions. One downside of such processes is that when formic acid is generated, it mixes with the salts. To overcome this the researchers deployed solid electrolytes that can conduct protons and which are made from insoluble polymers or inorganic compounds, eliminating the need for salts.
Commenting on the process, lead researcher Dr. Haotian Wang told Laboratory Manager magazine: “Formic acid is an energy carrier. It’s a fuel-cell fuel that can generate electricity and emit carbon dioxide—which you can grab and recycle again.”
Longer-term the process may assist with generating greater quantities of hydrogen for use with hydrogen fuel-cell cars.
The research was funded by the U.S. Department of Energy Office of Science User Facilities and it has been published in the journal Nature Energy. The paper is titled “Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices.”
